Altitude deviation. Miscom on altitude clearance between ATC and flight crew. Similarity of numbers. 21000 versus 22000 in clearance. Flight crew read back 21 and descended to that, but controller had said 22. No loss of separation.

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Attributes
ACN	338040
Time
Date	199606
Day	Fri
Local Time Of Day	1201 To 1800
Place
Locale Reference	atc facility : lwb
State Reference	WV
Altitude	msl bound lower : 21000 msl bound upper : 22000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zdc
Operator	general aviation : corporate
Make Model Name	Commercial Fixed Wing
Operating Under FAR Part	Part 91
Flight Phase	cruise other descent other
Flight Plan	IFR
Person 1
Affiliation	Other
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Experience	flight time total : 15125
ASRS Report	338040
Person 2
Affiliation	Other
Function	flight crew : first officer
Qualification	pilot : instrument pilot : atp
Experience	flight time last 90 days : 100 flight time total : 5000 flight time type : 1000
ASRS Report	338043
Events
Anomaly	altitude deviation : overshoot non adherence : clearance non adherence : far
Independent Detector	other controllera
Resolutory Action	controller : issued new clearance other
Consequence	Other
Supplementary
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

Flight departure operations at a high level during week, carrying passenger between new york area, washington, dc, area and lwb airport. This was second consecutive day for same crew, and possible fatigue was a factor, coupled with a need to meet a tight schedule. I was captain for this day, but not flying (PNF). Controller assigned a new altitude and PF initiated descent to altitude preset by me. At leveloff FL210, ATC controller announced 'you were assigned FL220, you are indicating FL210, state intentions.' as PNF, I responded 'I read back FL210, do you want FL220, we'll climb? He said no, take up heading and proceed to lwb. Of course, both of us (pilots) were flabbergasted at what happened, and are still wondering if we were in error and why this happened. I think fatigue, and stress may have led to insidious complacency, a clear day, quiet, little traffic, etc. After several hours of high density, low visibility, up and down operations in nyc area. This was a wake-up call no one will forget.

Original NASA ASRS Text

Title: ALTDEV. MISCOM ON ALT CLRNC BTWN ATC AND FLC. SIMILARITY OF NUMBERS. 21000 VERSUS 22000 IN CLRNC. FLC READ BACK 21 AND DSNDED TO THAT, BUT CTLR HAD SAID 22. NO LOSS OF SEPARATION.

Narrative: FLT DEP OPS AT A HIGH LEVEL DURING WK, CARRYING PAX BTWN NEW YORK AREA, WASHINGTON, DC, AREA AND LWB ARPT. THIS WAS SECOND CONSECUTIVE DAY FOR SAME CREW, AND POSSIBLE FATIGUE WAS A FACTOR, COUPLED WITH A NEED TO MEET A TIGHT SCHEDULE. I WAS CAPT FOR THIS DAY, BUT NOT FLYING (PNF). CTLR ASSIGNED A NEW ALT AND PF INITIATED DSCNT TO ALT PRESET BY ME. AT LEVELOFF FL210, ATC CTLR ANNOUNCED 'YOU WERE ASSIGNED FL220, YOU ARE INDICATING FL210, STATE INTENTIONS.' AS PNF, I RESPONDED 'I READ BACK FL210, DO YOU WANT FL220, WE'LL CLB? HE SAID NO, TAKE UP HDG AND PROCEED TO LWB. OF COURSE, BOTH OF US (PLTS) WERE FLABBERGASTED AT WHAT HAPPENED, AND ARE STILL WONDERING IF WE WERE IN ERROR AND WHY THIS HAPPENED. I THINK FATIGUE, AND STRESS MAY HAVE LED TO INSIDIOUS COMPLACENCY, A CLR DAY, QUIET, LITTLE TFC, ETC. AFTER SEVERAL HRS OF HIGH DENSITY, LOW VISIBILITY, UP AND DOWN OPS IN NYC AREA. THIS WAS A WAKE-UP CALL NO ONE WILL FORGET.

Data retrieved from NASA's ASRS site as of July 2007 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.